Recently, following the spread of the personal computer, a digital camera by which an image can be easily taken into the personal computer is spread. Further, a case where a digital camera is assembled into an information processing device such as a mobile computer, cell phone, Personal Digital Assistant (PDA) is also come into common use. Following such a spread of the digital camera, a more compact digital camera is required, and it is necessary that the imaging optical system is also further down-sized.
Further, as the imaging optical system of the digital camera, a zoom optical system is required, and in it, an optical system whose wide angle side is wider than before is required.
Accordingly, in order to make the zoom optical system wide angle of view and down-sized, in Japanese Laid-Open Patent publication No. 2001-174704, the five-groups composition in which the power arrangement of negative, positive, negative, positive, positive, in the order from an object side is made is disclosed, lens groups except the third lens group are moved to realize zooming, and a wide angle of view zoom lens of about 3 times is proposed. Further, in Japanese Laid-Open Patent publication No. 2004-271937, in the five groups composition in which the power arrangement of negative, positive, negative, positive, positive, in the order from an object side is made, each group is individually moved during zooming, and a wide angle of view zoom lens of about 5 times is proposed.
However, in the optical system written in Japanese Laid-Open Patent publication No. 2001-174704, the first lens group is moved during zooming, further, the effective diameter of the first lens group is large, and the size of the optical system becomes large for mounting it in the digital camera that is required to be down-sized. Further, the optical system written in Japanese Laid-Open Patent publication No. 2004-271937 is wide angle of view and the variable magnification ratio is large, however, the structure of the complicate drive mechanism of cam by which each lens group is individually moved during zooming becomes necessary, the image pick-up apparatus is large-sized, and further, the large drive force is necessary and the power consumption is increased.